1. Field of the Invention
The present invention relates to a device for starting an internal combustion engine of a motor vehicle.
2. Description of Related Art
Internal combustion engines of motor vehicles are usually started by a starter motor which is supplied with electrical current from a vehicle battery. Known starter motors include a solenoid switch via which a pinion that is driven by the starter motor is engaged with a ring gear attached to a flywheel of the internal combustion engine. In the starting position the ignition lock closes an electric circuit which causes current to flow through the solenoid switch, so that the pinion is moved forward against the ring gear via an engaging lever. As a rule, a tooth-to-tooth position occurs in which the pinion must be rotated in order to engage in a gap in the ring gear. Toward the end of the relay path the solenoid switch closes the main electrical circuit of the starter motor via a contact, as the result of which current flows through the starter motor and the starter motor starts to rotate. The pinion fully engages with the ring gear immediately after rotation starts. The starter motor thus drives the pinion, and via the pinion drives the ring gear of the internal combustion engine, which likewise starts to rotate. When the ignition key is released the relay circuit is interrupted, and the pinion is disengaged via a restoring spring.
It is known from published European patent document EP 0848159 to separately activate the solenoid switch and the starter motor via an electronic control device and two switching output stages in order to carry out the engaging process independently of the actual starting process. It is thus possible, for example, for the pinion to engage when the internal combustion engine is at a standstill, and for the actual starting process to be carried out only after a start request (turning of the ignition key) by the driver. This process is referred to as “pre-engagement.” In this manner, restarting of the vehicle may be accelerated, in particular during start-stop operation of the motor vehicle, since the pinion is already in the engaged position. However, the early engagement of the pinion when the internal combustion engine is at a standstill has the disadvantage that the engaging process produces a clearly audible clicking sound when the solenoid switch activates and the pinion strikes the ring gear axially, or, during engagement, rotates against a tooth flank of the ring gear. This is irritating and unpleasant for the driver.
It is therefore an object of the present invention to provide a device for starting an internal combustion engine in which the engagement noise level produced by the starter is significantly lower, and to further shorten the starting process.